The present invention relates to improved processes for the preparation of N,Nxe2x80x2-carbonyidiazoles by reaction of azolide salts with phosgene and for the preparation of azolide salts.
It is already basically known that N,Nxe2x80x2-carbonyldiazoles can be obtained if azoles are reacted with phosgene (see DE-B 10 33 210, Chem. Ber. 96, 3374 (1963), Org. Synth. Coll. Vol. IV, 201-204 (1968), and EP-A 692,476).
It is disadvantageous in all these processes that half of the azole employed is consumed as scavenger for the hydrogen chloride formed, and therefore only a maximum of 50% of the azole employed can be converted into the desired carbonyldiazole. This is a severe disadvantage, since azoles are expensive products and large azole consumption thus causes high production costs. Furthermore, the azole hydrochlorides are partially obtained in the form of a tacky precipitate, which can be separated off from the carbonyldiazole prepared only with difficulty. Finally, the azole hydrochloride formed as by-product must be disposed of, which causes additional costs.
The process for the synthesis of N,Nxe2x80x2-carbonyldiimidazole in accordance with U.S. Pat. No. 4,965,366 attempts to avoid these disadvantages by reacting imidazole with chlorotrimethylsilane in a first reaction step to give trimethylsilylimidazole. An amine (for example, 1,2-diaminoethane) is added at this step in order to scavenge the hydrogen chloride, and the resultant amine hydrochloride is filtered off and either fed to recovery of the amine or disposed of. The trimethylsilylimidazole formed in the reaction furthermore has to be purified by distillation before the further reaction. In the next step, the trimethylsilylimidazole is reacted with phosgene. In this reaction, chlorotrimethylsilane is re-formed, and can, after purification, be reused in the reaction. Disadvantages in this process are the many synthesis and purification steps and the fact that chlorotrimethylsilane is difficult to handle due to its hygroscopic and corrosive properties. In total, three assistants have to be employed for this N,N-carbonyldiimidazole synthesis, namely chlorotrimethylsilane, 1,2-diaminoethane, and sodium hydroxide solution. In addition, the amine, the imidazole, and the solvent required for the trimethylsilylimidazole synthesis have to be dried in a complex procedure.
A process has now been found for the preparation of N,Nxe2x80x2-carbonyl-diazoles of the formula (I) 
in which
X1, X2, and X3 independently of one another are each CR1 or nitrogen, where R1 is hydrogen or C1-C6-alkyl, and
R2 is hydrogen,
or in which
X2 is as defined above, and
X1 and X3 are CR1, where the R1 of each X1 is hydrogen or C1-C6-alkyl, and the R1 of each X3, together with R2 of the same diazole ring, forms a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
comprising reacting azolide salts of the formula (II) 
xe2x80x83in which
M⊕ is an equivalent of an alkali metal or alkaline earth metal cation or a quaternary onium ion of the formula (III)
[YR3R4R5R6]⊕xe2x80x83xe2x80x83(III),
in which
Y is phosphorus or nitrogen, and
R3, R4, R5, and R6 independently of one another are each C1-C20-alkyl, phenyl, benzyl, or ethylbenzyl, and
the other symbols are as defined for the formula (I), with phosgene in an aromatic compound or an ether as solvent.